Keep OpenAI Agents traces connected across Temporal execution

[1fanwang]

What was changed

OpenAI Agents traces keep their root metadata and parent links when a workflow and its activities share a worker. Workers use remote parent context instead of recording caller-span replicas. Callbacks finish in their starting Context, and trace completion restores the caller's context.

Why?

Previously, workers could replace the caller's spans and leave missing parents. Callbacks also logged Failed to detach context and left finished spans current, so later work could attach to the wrong parent. Child-workflow command ordering stays unchanged.

Checklist

1. Fixes temporalio/sdk-python#1852, temporalio/sdk-python#1853, and temporalio/sdk-python#1855.
2. The live repro uses TestModel with Temporal Server 1.31.2, Python 3.12.13, SDK 1.32.0, Agents 0.19.4 and OpenInference 1.6.1. It makes no model API calls.
3. The changelog is updated.

After the documented SDK build, start the server and run the test in another terminal. The before run applies this PR's tests to unchanged main; the after run uses this PR.

temporal server start-dev --ip 127.0.0.1 --port 17352 --headless
env -u OPENAI_API_KEY PYTHONUNBUFFERED=1 uv run --no-sync python -m pytest tests/contrib/openai_agents/test_openai_tracing.py -k 'otel_remote_context_preserves_root or otel_callback_spans_restore_context' -E 127.0.0.1:17352 -q -s --tb=short --color=no

Raw logs

Before:

E   AssertionError: The original client root was not exported
ValueError: <Token var=<ContextVar name='current_context' default={} at 0x10a5412b0> at 0x111763a40> was created in a different Context
Retained roots/spans/tokens: [(0, 1, 1), (0, 2, 2), (0, 3, 3)]
Caller context restored: [False, False, False]
         3 failed

After:

Missing parents: []
Retained roots/spans/tokens: [(0, 0, 0), (0, 0, 0), (0, 0, 0)]
Caller context restored: [True, True, True]
         3 passed